Acrocanthosaurus

“High-spined lizard (from) Atoka”

At nearly 40 feet long, Acrocanthosaurus atokensis—or Acro—was one of North America’s largest predators (100 – 115 mya). With a large head, powerful back legs, and relatively small arms, it looked very similar to a Tyrannosaurus rex. However, unlike a T. rex, Acro had tall spinal processes, which supported a strong muscle ridge or “sail”. Scientists are unsure what purpose it served. The ridge may have supported its large body and/or powerful leg muscles.

Other animals use similar structures when attracting mates. However, Acro’s sail may have also been a defensive mechanism instead. For example, it might have used the sail to appear larger when facing rival dinosaurs. Acro may have also used its sail to regulate its body temperature.

Acro preferred to stalk its prey in open, arid environments or low-lying riverbeds. The bulk of its diet was probably made up of smaller, plant-eating dinosaurs like Tenontosaurus. Footprints in the Glen Rose, Texas trackway suggest that Acro may have even hunted larger dinosaurs like Sauroposeidon. A full grown Sauroposeidon was over 100 feet long and it would not have been easy for Acro to take down.

McCurtain County “bones”

The first remains of an Acrocanthosaurus were discovered in 1940 by J. Willis Stovall and Wann Langston, Jr. near Atoka, Oklahoma. Other fossils have been found in Texas, Utah, and perhaps Maryland. However, the most complete skeleton was unearthed by amateur paleontologists Cephis Hall and Sid Love in 1983, less than twenty miles from the Museum. Over fifty percent of the fossil was recovered—including the entire skull. Their find would change everything paleontologists knew about Acro.

Unfortunately, the fossil was extremely fragile. Organic matter in prehistoric remains is usually replaced by stable quartz compounds. However, this specimen was composed of iron and sulfur compounds, including marcasite and pyrite. The former crumbles in open air when in a non-crystalline state. The latter can emit sulfuric acid fumes when removed. The high humidity levels only worsened the situation. The two men needed more help.

They contacted Allen and Fran Graffham of Geological Enterprises in Ardmore, OK. With their help, the remains were moved to the Black Hills Institute for Geological Research in South Dakota. The Institute built a dedicated lab space for the remains and the fossil was saved a few years later. It was eventually sold to the North Carolina Museum of Natural History.